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Volume 22, issue 10 | Copyright
Hydrol. Earth Syst. Sci., 22, 5143-5158, 2018
https://doi.org/10.5194/hess-22-5143-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Oct 2018

Research article | 04 Oct 2018

Why has catchment evaporation increased in the past 40 years? A data-based study in Austria

Doris Duethmann and Günter Blöschl Doris Duethmann and Günter Blöschl
  • Institute for Hydraulic and Water Resources Engineering, Vienna University of Technology, Karlsplatz 13/223, 1040 Vienna, Austria

Abstract. Regional evaporation has increased in many parts of the world in the last decades, but the drivers of these increases are widely debated. Part of the difficulty lies in the scarcity of high-quality long-term data on evaporation. In this paper, we analyze changes in catchment evaporation estimated from the water balances of 156 catchments in Austria over the period 1977–2014 and attribute them to changes in atmospheric demand and available energy, vegetation, and precipitation as possible drivers. Trend analyses suggest that evaporation has significantly increased in 60% of the catchments (p ≤ 0.05) with an average increase of 29±14mmyr−1decade−1standard deviation) or 4.9±2.3%decade−1. Pan evaporation based on 24 stations has, on average, increased by 29±5mmyr−1decade−1 or 6.0±1.0%decade−1. Reference evaporation over the 156 catchments estimated by the Penman–Monteith equation has increased by 18±5mmyr−1decade−1 or 2.8±0.7%decade−1. Of these, 2.1% are due to increased global radiation and 0.5% due to increased air temperature according to the Penman–Monteith equation. A satellite-based vegetation index (NDVI) has increased by 0.02±0.01decade−1 or 3.1±1.1%decade−1. Estimates of reference evaporation accounting for changes in stomata resistance due to changes in the NDVI indicate that the increase in vegetation activity has led to a similar increase in reference evaporation as changes in the climate parameters. A regression between trends in evaporation and precipitation yields a sensitivity of a 0.22±0.05mmyr−2 increase in evaporation to a 1mmyr−2 increase in precipitation. A synthesis of the data analyses suggests that 43±15% of the observed increase in catchment evaporation may be directly attributed to increased atmospheric demand and available energy, 34±14% to increased vegetation activity, and 24±5% to increases in precipitation.

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We analyze changes in catchment evaporation estimated from the water balances of 156 catchments in Austria over 1977–2014, as well as the possible causes of these changes. Our results show that catchment evaporation increased on average by 29 ± 14 mm yr−1 decade−1. We attribute this increase to changes in atmospheric demand (based on reference and pan evaporation), changes in vegetation (quantified by a satellite-based vegetation index), and changes in precipitation.
We analyze changes in catchment evaporation estimated from the water balances of 156 catchments...
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